The present invention relates generally to drilling. More particularly, the invention relates to an apparatus and method for drilling a hole (e.g., during machining drill operations).
Long xe2x80x9cchipsxe2x80x9d formed during a hole-making operation (e.g., drilling, reaming, boring, etc.) may cause numerous problems in a machining operation. The chips may tangle around a drill tooling thereby requiring cleaning downtime after each operation. Failure to adequately remove long chips may shorten the tool life and may result in degraded holes that do not meet specification. Therefore, it would be desirable for a drilling method and apparatus to provide long chip removal or elimination.
In an effort to deal with long chip formation, a xe2x80x98peckingxe2x80x99 cycle strategy has been developed. The pecking cycle may involve repeatedly and completely retracting the drill tooling from a partially formed hole. For example, U.S. Pat. No. 5,833,404 issued Nov. 10, 1998 to Johnson et al. is an example of a portable peck feed drilling system. In the Johnson patent, operation of the drilling system includes advancing a rotating drill bit into a workpiece followed by full retraction to xe2x80x9chomexe2x80x9d position. The process may be repeated to drill to a desired depth. The pecking cycle demonstrated by the Johnson and other patents may overcome several problems associated with long chip formation.
A shortcoming associated with pecking cycle drilling operations relates to overall operation time. The need for full and repeated removal of the drill tooling from a forming hole increases the overall operation time with each pecking cycle. In addition, some pecking cycles may adversely affect the surface finish of the hole. For example, tool markings may be made within the hole when the drill tooling is fed back at a rapid feed-rate after each cycle. This may result in a degraded hole that does not meet specification. To avoid making tool markings, the drill tooling may be fed back into the forming hole at a slower rate thereby further increasing the pecking cycle time. As such, it would be desirable for a drilling method and apparatus to provide short overall operation time while maintaining hole specification.
Therefore, it would be desirable to provide a method and apparatus for drilling a hole that overcomes the aforementioned and other disadvantages.
One aspect of the present invention provides a drilling apparatus including means for rotating a drill bit, and means for advancing the rotating drill bit into a workpiece to a first depth. The drilling apparatus further includes means for dwelling the drill bit within the workpiece at the first depth for a dwell time, and means for further advancing the rotating bit to a second depth after the dwell time has expired. The apparatus may include means for flowing a fluid adjacent the rotating drill bit. The apparatus may further include means for determining at least one drilling parameter, and means for controlling at least one of the first depth, the dwell time, and the second depth based on the drilling parameter.
Another aspect of the invention provides a method for drilling a hole in a workpiece. The drilling method includes rotating a drill bit, and advancing the rotating drill bit into the workpiece to a first depth. The method further includes dwelling the drill bit within the workpiece at the first depth for a dwell time, and further advancing the rotating bit to a second depth after the dwell time has expired. The dwell time may be estimated from a dwell equation. A fluid may be flowed adjacent the rotating drill bit. At least one drilling parameter may be determined, and at least one of the first depth, the dwell time, and the second depth may be controlled based on the drilling parameter. The drilling parameters may be determined based on a control sequence and/or a database including at least one drilling factor. The drilling factor may include a workpiece material characteristic, a desired hole geometry, a drill bit characteristic, and a fluid flow characteristic.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention, rather than limiting the scope of the invention being defined by the appended claims and equivalents thereof.